After considerable difficulty he determined that the relative weight of a cubic inch of water and mercury was about one to fourteen, and computing from other known weights he determined that "when a column of quicksilver thirty inches high is sustained in the barometer, as it frequently happens, a column of air that presses upon an inch square near the surface of the earth must weigh about fifteen avoirdupois pounds."(4) As the pressure of air at the sea-level is now estimated at 14.7304 pounds to the square inch, it will be seen that Boyle's calculation was not far wrong.
From his numerous experiments upon the air, Boyle was led to believe that there were many "latent qualities" due to substances contained in it that science had as yet been unable to fathom, believing that there is "not a more heterogeneous body in the world." He believed that contagious diseases were carried by the air, and suggested that eruptions of the earth, such as those made by earthquakes, might send up "venomous exhalations" that produced diseases.

He suggested also that the air might play an important part in some processes of calcination, which, as we shall see, was proved to be true by Lavoisier late in the eighteenth century.

Boyle's notions of the exact chemical action in these phenomena were of course vague and indefinite, but he had observed that some part was played by the air, and he was right in supposing that the air "may have a great share in varying the salts obtainable from calcined vitriol."(5) Although he was himself such a painstaking observer of facts, he had the fault of his age of placing too much faith in hear-say evidence of untrained observers.

Thus, from the numerous stories he heard concerning the growth of metals in previously exhausted mines, he believed that the air was responsible for producing this growth--in which he undoubtedly believed.

The story of a tin-miner that, in his own time, after a lapse of only twenty-five years, a heap, of earth previously exhausted of its ore became again even more richly impregnated than before by lying exposed to the air, seems to have been believed by the philosopher.
As Boyle was an alchemist, and undoubtedly believed in the alchemic theory that metals have "spirits" and various other qualities that do not exist, it is not surprising that he was credulous in the matter of beliefs concerning peculiar phenomena exhibited by them.